The nematode, Caenorhabditis elegans, has been identified as a "high connectivity" animal for cellular development. This very small, simple animal has been widely adopted for experimental study due to its excellent genetics and accessible cell biology. The complete genome of the worm has been published, and most of the adult anatomy has been reconstructed from electron micrographs of serial thin sections. However, EM techniques are not widely utilized by the C. elegans community, and most previous EM data are not easily accessed. The Center for C. elegans Anatomy concentrates on extending the EM methods on C. elegans, particularly to 1) study cellular changes during normal development and in mutant animals, and 2) conduct EM-immunocytochemical and histochemical studies to localize antigens or molecules at the ultrastructural level. Such studies are being conducted in close collaboration with NIH- and NSF-funded laboratories, in fulfillment of their existing experimental aims. In addition, the Center is 3) publishing detailed information regarding the anatomy of the nematode in the form of annotated TEM and light micrographs. Information is available on the Internet on our WormAtlas website, by ftp, on CDs and DVDs, and soon will be published in book form. Where necessary, the Center is 4) testing new EM methods for C. elegans, and conducting new EM surveys of the wild type anatomy at key developmental stages to supplement the Atlas, and to fill gaps in our general knowledge. The Center also provides 5) training in TEM methods so that more C. elegans labs can conduct their own EM studies. Many disease-related gene sequences are known in the C. elegans genome; the TEM pathology of genetic mutations in nematode is often helpful in discovering the function of equivalent gene products in man. This R24 application was first funded and the Center opened in Feb. 1998; we request five years of funding to continue building our capabilities to serve the scientific community.